Why is it that commercial passenger aircraft that fly through dangerous areas don't carry some sort of electronic counter measure to defend themselves from missiles? Between terrorism and the various war zones dotting the globe, it seems like it would be prudent for airliners to have them. At least for aircraft that are flying in places that are possibly dangerous.

I've been thinking that it's probably a lot of expense and weight for something that isn't terribly likely to happen, but I wondered if there might be more to the answer or if, at very least, someone could add some details to my assumption. A good cost/benefit analysis would be appreciated if anyone is familiar with the cost of operating such a system.

Odds are greater the threat will be internal (parts failure or on board physical terrorist) vs. external (ground to air, air to air). Though there have been more than one airliner shot down, more have been lost due to internal threats. Cost vs risk. The risk of being shot down, in compared to the massive number of miles flown is infinitesimal compared to a terrorist on board which can be compared to engine/elect/hyd failures.
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CGCampbellJul 18 '14 at 18:14

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@CGCampbell: Well, the solution to KAL007 and KAL902 was introduction of GPS as navigational error leading the aircraft into closed airspace was major part of such incidents.
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Jan HudecJul 18 '14 at 18:39

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Modern SAMs cannot be jammed easily. Besides radar they use a variety of thermal, acoustic, optical, wake detection sensors. A 75 m long airliner flying straight below Mach 1 would be hard to miss. Nothing could have saved MH17, once the decision was made to destroy it.
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staliJul 19 '14 at 18:34

@stali If you can work that into the selected answer as a suggested edit, I think it would be a good idea. You have a good point. And at this point I'm really just trying to get everyone to put the strongest comments into the accepted answer.
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Jay CarrJul 21 '14 at 13:49

You are assuming that all missiles use radar, which is not the case
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Steve KuoJul 21 '14 at 14:37

4 Answers
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El Al (and other Israeli) aircraft are equipped with infra-red countermeasures since fire at Arkira B757 in Mombasa in 2002. Infra-red counter-measures are relatively simple (it has a small radar to detect missiles and if one is detected, dispenses burning decoys), so it can be mounted on almost any aircraft. The system however poses additional fire risk (the flares have to burn very hot and the system has to be able to ignite them), so it is only used in areas where risk of terrorist attack is high. Switzerland (and possibly other countries) even prohibit it on their territory. Apparently laser-based system is in development to resolve the fire issue, but it will still only work against IR-guided missiles.

But for radar guided missiles like the Buk system probably involved in this incident there only seem to be three defences:

Hit the tracking radar with your own missile (like AGM-88 HARM) before they hit you. Fighter aircraft is obviously needed to carry it, though most fighter types could be used as they only need radar detector and suitable hardpoints.

Generate sufficiently intense microwave signal that it overdrives the detector in the missile head and effectively blinds it. This is heavy, expensive and requires power (not outside the range of common aircraft generators, but the increased fuel burn would probably be noticeable), so even most fighters don't have it. Instead the system (like AN/ALQ-99) is mounted on special-purpose aircraft like EF-111A Raven that gets included in attack group trying to penetrate enemy territory with heavy air defences.

Minimizing radar cross-section, ie. stealth. That requires completely different designs that are aerodynamically less efficient, because the funny shapes are necessary part of being stealth and that are not trackable by ATC surveillance radars.

While the second would be technically possible (E-4B, an airborne command centre, and VC-25, the Air Force One, are modified Boeing 747s and both have counter-measures against both IR-guided and radar-guided missiles), those modifications would be a heavy, expensive and complex protection against something that has only happened a few times.

And the third would have too many disadvantages. It would hide the aircraft from ATC surveillance radars that have averted many more accidents than were caused by missiles and it would require new, less efficient designs that would be massively expensive. Just few month ago we wanted MH-370 to be seen by radars. We can't have both.

Staying away from the war zones is a safer option anyway and is normally possible. In this case likely explanation why MH-17 didn't is that the Ukrainian authorities were not aware that the rebels have this air defence system, assumed they only have a lighter-weight one (those are often usable to about 20000'; the military aircraft shot down on previous days were lower) and only closed the airspace up to FL320 rather than completely.

"Obviously neither is an option for regular airliners" - why is this obvious? I think that's what the question is asking.
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user2168Jul 18 '14 at 18:49

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"Why is advanced weaponry obviously not an option for regular airliners?" Because the weapon will one day be accidentally fired, be stolen by terrorists, explode due to a system failure, explode during an otherwise minor accident, be fired by a resentful pilot, be fired at a harmless radar station that the pilots thought was targetting them, be fired at a friendly military radar that mistook the airliner for an intruder, etc. etc.
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DJClayworthJul 18 '14 at 19:44

I'll add a couple more points about something like the HARM missile. It's a race between two weapons which both operate at around Mach 3--killing the guidance radar before the missile gets you is hard enough for the guys whose job it is to hunt the SAMs, let alone for a jetliner. Furthermore, it takes a lot of electronics and a skilled operator to figure out exactly what the target is and tell the HARM that.
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Loren PechtelJul 19 '14 at 4:11

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@Articuno putting any weaponry on civilian airliners would mean that they are not civilian airliners anymore. Convention of International Civil Aviation article 35 prohibits any "munitions of war or implements of war", even carrying them as cargo. If an airliner would be equipped with air-to-ground missiles, then it would require explicit permission and flight coordination from each and every country it flies over, as any other scheduled military flights over foreign space; and they'd have full rights to arbitrarily deny it, unlike civilian flights.
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PeterisJul 19 '14 at 13:07

@JayCarr: Since ICAO didn't seem to protest against Israeli airlines installing flares in some of their aircraft these apparently are not considered weapons. USA and Switzerland do not want these aircraft on their territories, but it is due to increased fire risk (system that blinds the missile by bright infra-red laser instead seems to be in development to resolve that), not due to being weapons.
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Jan HudecJul 21 '14 at 14:02

Surface-to-air missile attacks on airliners at cruising altitude are vanishingly rare: there have only been three known attacks in the past half-century (MH-17, IR-655, and probably S7-1812). Any protection system needs to take that into account -- any safety system needs to be justified in terms of cost, weight, and safety -- it needs to save more lives than it costs.

Direct jamming. Suppose you stick an AN/ALQ-99 jamming pod on the airplane. That's 6000 extra pounds, a good deal of drag, and a bunch of parts that can break off, catch fire, or otherwise be a hazard.

Active countermeasures. Stick an AGM-88 HARM missile on the plane. Now, your anti-radar missile isn't much faster than the radar-guided missile trying to shoot you down, so for reasonable safety, you need to launch as soon as you get painted by the tracking radar. What do you suppose the odds are that a twitchy co-pilot acting as ECM/weapons officer is going to launch against an innocent control tower? How many weather radars are you willing to destroy to save that one airplane every 20 years? Are you sure that missile will never malfunction on the launching rack and destroy the airplane?

Stealth. Hiding from radar-guided missiles means you're also hiding from traffic-control radar. How often are crashes prevented by that radar? I bet it's more than one every twenty years.

The benefit is roughly one less airplane crash every 20 years. That means the cost, both in terms of money and in terms of risk, needs to be very, very low.

+1 for adding what should obvious Hiding from radar-guided missiles means you're also hiding from traffic-control radar.
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user2338816Jul 19 '14 at 12:07

Is it ironic that people were complaining about MH-370 not being seen by radar, and now MH-17 because it was?
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CGCampbellJul 19 '14 at 19:11

@CGCampbell By very definition if I'm not mistaken.
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Jay CarrJul 21 '14 at 13:58

I was wondering if the author could see about adding point 3 to the accepted answer as a suggested edit (since I think points 1 and 2 are more or less covered). I'm trying to get all the best answer into once place...
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Jay CarrJul 21 '14 at 13:59

+1 for "vanishingly rare": the extreme unlikeliness of such events seems to escape most people. Downing a civilian airplane is guaranteed to make international news, and airplanes are special in how far people are willing to go in suggesting counter-measures to unlikely events while also being very much against many effective counter-measures for rather likely road traffic deaths...
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romkynsJan 9 at 22:51

It's a good assumption, but do you have any facts or figures on that?
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Jay CarrJul 18 '14 at 17:40

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@JayCarr I don't think you can have facts or figures about the risk-aversion curve of an airline and what they find "worth it". But, we could at least report what the costs would be.
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user2168Jul 18 '14 at 17:54

Honestly, 150 000 people die every day. It simply isn't worth it to install countermeasures, because of the tiny probability that 300 people will die because Russia need reason to start offensive. I know, It's a cruel world...

It is. It says that for manufacturer, 300 people are worth less than good countermeasures.
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user2486570Jul 19 '14 at 0:14

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@user2486570 300 people are killed by cars in the USA every three days or so. Would you install an expensive, heavy device on every car in the USA to prevent that? Even though the overwhelming majority of cars will never be involved in a fatal accident? Even though a car is probably much more likely to be involved in a fatal accident than a civilian airliner is to be shot down by a SAM at 33,000ft? Or would you just encourage people to drive more carefully?
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David RicherbyJul 19 '14 at 0:53

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While I can accept that the world is cruel, I should point out that it's never stopped us, as people, from trying to lessen the cruelty as much as possible.
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Jay CarrJul 21 '14 at 14:02